Massive Protostars in the Infrared Dark Cloud MSXDC G034.43+00.24

We present a multiwavelength study of the infrared dark cloud MSXDC G034.43+00.24. Dust emission, traced by millimeter/submmillimeter images obtained with the IRAM, JCMT, and CSO telescopes, reveals three compact cores within this infrared dark cloud with masses of 170-800 M☉ and sizes <0.5 pc. Spitzer 3.6-8.0 μm images show slightly extended emission toward these cores, with a spectral enhancement at 4.5 μm that probably arises from shocked H2. In addition, the broad line widths (ΔV ~ 10 km s-1) of HCN (4-3) and CS (3-2) and the detection of SiO (2-1), observed with the JCMT and IRAM telescopes, also indicate active star formation. Spitzer 24 μm images reveal that each of these cores contains a bright, unresolved continuum source; these sources are most likely embedded protostars. Their millimeter-to-mid-IR continuum spectral energy distributions reveal very high luminosities, 9000-32,000 L☉. Because such large luminosities cannot arise from low-mass protostars, MSXDC G034.43+00.24 is actively forming massive (~10 M☉) stars.